The ability to control nanoscale imperfections in superconducting wires results in materials with unparalleled and customized performance, according to a new study from the Department of Energy’s Oak Ridge National Laboratory.
Applications for superconducting wires, which carry electricity without resistance when cooled to a critical temperature, include underground transmission cables, transformers and large-scale motors and generators. But these applications require wires to operate under different temperature and magnetic field regimes.
A team led by ORNL’s Amit Goyal demonstrated that superconducting wires can be tuned to match different operating conditions by introducing small amounts of non-superconducting material that influences how the overall material behaves. Manipulating these nanoscale columns — also known as defects — allows researchers to exert control over the forces that regulate the wires’ superconducting performance.
– See more at: http://www.ornl.gov/ornl/news/news-releases/2013/ornl-superconducting-wire-yields-unprecedented-performance#sthash.E12GQn9l.dpuf
This figure shows the critical current, Ic, and engineering critical current density, JE, in a superconducting wire as a function of applied magnetic field orientation at 65 Kelvin and 3 Tesla. The top curve shows results from a newly published ORNL study. The other two curves are from previously reported record values. A minimum JE of 43.7 kiloamperes/cm2 (assuming a 50 micron thick stabilizer layer) and a minimum Ic of 455 Amperes/cm was obtained for all applied field orientations. This is the highest reported performance for a superconductor wire or a film on a technical substrate
“Not only can we introduce these nanocolumn defects within the superconductor and get enhanced performance, but we can optimize the performance for different application regimes by modifying the defect spacing and density,” Goyal said.
A wire sample grown with this process exhibited unprecedented performance in terms of engineering critical current density, which measures the amount of current the wire can carry per unit cross-sectional area. This metric more accurately reflects the real-world capabilities of the material because it takes into account the wire’s non-superconducting components such as the substrate and the buffer and stabilizer layers, Goyal said.
“We report a record performance at 65 Kelvin and 3 Tesla, where most rotating machinery applications like motors and generators are slated to operate,” he said.
The paper reports a minimum engineering critical current density at all applied magnetic field orientations of 43.7 kiloamperes/cm2, which is more than twice the performance level needed for most applications. This metric assumes the presence of a 50-micron-thick copper stabilizer layer required in applications.
ABSTRACT – We report microstructural design via control of BaZrO3 (BZO) defect density in high temperature superconducting (HTS) wires based on epitaxial YBa2Cu3O7-δ (YBCO) films to achieve the highest critical current density, Jc, at different fields, H. We find the occurrence of Jc(H) cross-over between the films with 1–4 vol% BZO, indicating that optimal BZO doping is strongly field-dependent. The matching fields, Bφ, estimated by the number density of BZO nanocolumns are matched to the field ranges for which 1–4 vol% BZO-doped films exhibit the highest Jc(H). With incorporation of BZO defects with the controlled density, we fabricate 4-μm-thick single layer, YBCO + BZO nanocomposite film having the critical current (Ic) of ~1000 A cm−1 at 77 K, self-field and the record minimum Ic, Ic(min), of 455 A cm−1 at 65 K and 3 T for all field angles. This Ic(min) is the largest value ever reported from HTS films fabricated on metallic templates.